Text-book of comparative anatomy . FIG. 59.—Part of a section through Halisarca lobularis, after F. E. Schulze. ec, Ectodermalpavement epithelium ; gh, gastral cavity ; in, mesoderm ; p, pores ; gk, ciliated chambers ; zk, affer-ent canals ; o, eggs in different stages of segmentation. cells. There are uniradiate, triradiate, quadriradiate, sexiradiate, multi-radiate forms, stars, spheres, etc. The skeleton of a sponge may con-sist of only one sort ofspicule, or two or moresorts may occur together. The single spicules lieeither loosely near eachother, or are cementedtogether into coherentframe
Text-book of comparative anatomy . FIG. 59.—Part of a section through Halisarca lobularis, after F. E. Schulze. ec, Ectodermalpavement epithelium ; gh, gastral cavity ; in, mesoderm ; p, pores ; gk, ciliated chambers ; zk, affer-ent canals ; o, eggs in different stages of segmentation. cells. There are uniradiate, triradiate, quadriradiate, sexiradiate, multi-radiate forms, stars, spheres, etc. The skeleton of a sponge may con-sist of only one sort ofspicule, or two or moresorts may occur together. The single spicules lieeither loosely near eachother, or are cementedtogether into coherentframeworks. The same isthe case with horn ordinary bath spongeis only a framework of suchhorn fibres; it is merelythe skeleton of a marineanimal (Fig. 56).A nervous system is not yet with certainty proved to exist in thePorifcm. Reproduction is either asexual or sexual. Asexual reproduction takes place by external or internal buddingor gemmation. External gemmation.—A sponge may put out buds at various. FIG. CO.—Various forms of skeletal spiculaefrom Sponges. II PORIFERA G5 points of the body surface. These, without detaching themselves,grow larger, and can in their turn form buds. Sponge colonies thusarise. As buds may at various points grow together, the colony itselfmay again have the appearance of a plexus or framework. The holesand interspaces of such a colony may then again assume the characterof a canal system (pseudo-canals). These must, however, accordingto their origin, be sharply distinguished from the real canal systemwhich runs through the walls of every sponge individual Separatesponge individuals may also fuse and form colonies. The number ofoscula generally corresponds with the number of individuals whichform the colony (Fig. 56, o). In the so-called internal gemmation groups of cells calledgemmulse detach themselves from the sponge body, and after aperiod of rest develop into complete sponges. Observers differ as tothe finer processes which take pla
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
